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What is the structure of the crew documentation used in flight for a commercial aircraft?
Common documentation easily found online (using A320 family as an example):

Flight crew operating manual (FCOM, multiple volumes)
Flight crew training manual (FCTM)
Standard operating procedures (SOP)
Quick reference handbook (QRH)

(Source)
What are they used for? What are the other major documents necessary to fly? Do they differ with manufacturers or airlines? Are they available on paper or display?

FCOM: This document has everything the flight crew might need to know about the aircraft during flight. It must be available on board and pilots refer to it for anything they don't want to, or shouldn't, rely on their memory for, mainly performance calculations and troubleshooting. It is provided by the aircraft manufacturer, but customized according to equipment of each particular airframe and SOP of the particular operator.
FCTM: This document describes what the flight crew must regularly train, usually on the simulator. It does not have to be on board.
SOP: This document describes the operation side of things. There may be additional restrictions on acceptable clearances, rules for using derated take-off thrust, communication protocol towards cabin crew etc. This is created by the operator. The procedure side of things is usually uniform across the fleet, but there are also restrictions pertaining to particular aircraft. Should be available on board.
QRH: Basically excerpt from the above documents containing checklists and tables, so they are easy to find when they are needed, usually when things go wrong. Of course, should be on board.

The documents legally required on-board differ by jurisdiction. I can only speak to the case here in the US which falls under the FAA. If the flight is between two jurisdictions there may be local regulations to comply with at your destination as well. For example if leaving the US all onboard must have their passports as well as any pertinent custom forms.

What are they used for?

Generally these documents are all used for reference. Here in the US its generally forbidden to read personal material in the cockpit however the pilots are free to read documentation relating to the aircraft and operations. They may chose to use time in flight to read up on things.
These documents also include emergency procedures that the crew may need to use in the event of a failure.

What are the other major documents necessary to fly?

Aside from what the plane needs the crew must also have current medical certificates and pilots license on their persons.
If we take a look at FAR 121.135

(a) Except as provided in paragraph (c) of this section, no
  certificate holder may operate an aircraft unless that aircraft—

(1)
    Is registered as a civil aircraft of the United States and carries an
    appropriate current airworthiness certificate issued under this
    chapter; and
(2) Is in an airworthy condition and meets the applicable
    airworthiness requirements of this chapter, including those relating
    to identification and equipment.

(b) A certificate holder may use an
  approved weight and balance control system based on average, assumed,
  or estimated weight to comply with applicable airworthiness
  requirements and operating limitations.
(c) A certificate holder may
  operate in common carriage, and for the carriage of mail, a civil
  aircraft which is leased or chartered to it without crew and is
  registered in a country which is a party to the Convention on
  International Civil Aviation if—

(1) The aircraft carries an
    appropriate airworthiness certificate issued by the country of
    registration and meets the registration and identification
    requirements of that country;
    (2) The aircraft is of a type design
    which is approved under a U.S. type certificate and complies with all
    of the requirements of this chapter (14 CFR Chapter 1) that would be
    applicable to that aircraft were it registered in the United States,
    including the requirements which must be met for issuance of a U.S.
    standard airworthiness certificate (including type design conformity,
    condition for safe operation, and the noise, fuel venting, and engine
    emission requirements of this chapter), except that a U.S.
    registration certificate and a U.S. standard airworthiness certificate
    will not be issued for the aircraft;
    (3) The aircraft is operated by
    U.S.-certificated airmen employed by the certificate holder; and (4)
    The certificate holder files a copy of the aircraft lease or charter
    agreement with the FAA Aircraft Registry, Department of
    Transportation, 6400 South MacArthur Boulevard, Oklahoma City, OK
    (Mailing address: P.O. Box 25504, Oklahoma City, OK 73125).

Do they differ with manufacturers or airlines?

Airlines may publish excess documentation and checklists that meet or exceed the manufacture specifications this some airlines may have slightly varying procedures. Aircraft makers must publish documentation for the aircraft that includes its operational limitations you can find a good chunk of the regulations in the FAR's here. Specifically,

§23.1581   General.
(a) Furnishing information. An Airplane Flight Manual must be
  furnished with each airplane, and it must contain the following:
(1) Information required by §§23.1583 through 23.1589.
(2) Other information that is necessary for safe operation because of
  design, operating, or handling characteristics.
(3) Further information necessary to comply with the relevant
  operating rules.
(b) Approved information. (1) Except as provided in paragraph (b)(2)
  of this section, each part of the Airplane Flight Manual containing
  information prescribed in §§23.1583 through 23.1589 must be approved,
  segregated, identified and clearly distinguished from each unapproved
  part of that Airplane Flight Manual.
(2) The requirements of paragraph (b)(1) of this section do not apply
  to reciprocating engine-powered airplanes of 6,000 pounds or less
  maximum weight, if the following is met:
(i) Each part of the Airplane Flight Manual containing information
  prescribed in §23.1583 must be limited to such information, and must
  be approved, identified, and clearly distinguished from each other
  part of the Airplane Flight Manual.
(ii) The information prescribed in §§23.1585 through 23.1589 must be
  determined in accordance with the applicable requirements of this part
  and presented in its entirety in a manner acceptable to the
  Administrator.
(3) Each page of the Airplane Flight Manual containing information
  prescribed in this section must be of a type that is not easily
  erased, disfigured, or misplaced, and is capable of being inserted in
  a manual provided by the applicant, or in a folder, or in any other
  permanent binder.
(c) The units used in the Airplane Flight Manual must be the same as
  those marked on the appropriate instruments and placards.
(d) All Airplane Flight Manual operational airspeeds, unless otherwise
  specified, must be presented as indicated airspeeds.
(e) Provision must be made for stowing the Airplane Flight Manual in a
  suitable fixed container which is readily accessible to the pilot.
(f) Revisions and amendments. Each Airplane Flight Manual (AFM) must
  contain a means for recording the incorporation of revisions and
  amendments.
Are they available on paper or display?

Depends on the carrier, a great deal of movement to iPads and the such has seen the digitization of many things.

Where do you mention any of the documents specifically listed in the question? FCOM is apparently the same thing as AFM, but what about the rest?

I will do some more research on the ones listed, this was an answer to the "other documents and those legally required" aspect of the question


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Flight Mode in cellphones and in Flight WiFi access
More and more flights have in flight wifi. On the other hand, the standard pre flight announcement still tells to switch off phones or put them in flight mode.
So, once the in flight wifi is turned on during cruise, is it axiomatic that it is ok to turn flight mode off? I've heard some announcements say to connect to the wifi but still keep the cell signal off.  What's the electronics safety protocol regarding this?
As soon as I turn flight mode off, the phone's GSM chip is going to start hunting for a signal, correct?

@ymb. Ok I will remove the reference to phone settings if we are a stickler for that. But the core of the question, I hope you agree, is about aviation electronic usage  rules and not at all about phones in particular. If you can say, yes, this can be done, I can go and ask on the Android forums. But I really don't think this more to do with phones than aviation.

@ymb1 Ok, please go ahead and delete if if you think it is off topic.

@ymb1 That's GPS. I'm talking about the GSM signal here.

Let us continue this discussion in chat.

You need to be in flight mode to disable cell connection. That will turn off WiFi but, at least on my phone, you can turn WiFi back on without leaving flight mode.

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Has reversing the active runway direction ever led to lined-up aircraft taxiing to the other end of the runway?
I was in an aircraft yesterday waiting for its turn in the departure queue on the taxiway and noticed that the windsock was showing a direction approximately 30 degrees but directed along the direction we were entering the runway in. i.e. The parallel component would point in the take-off direction & not against it.
Made me wonder: Are there instances when lined up aircraft have to be made to taxi to the other end of a runway due to a last minute wind direction reversal?
Never happened to me, nor seen it mentioned in any ATC conversations / videos online so made me wonder.
Of course, if the parallel component is smaller than the allowable tailwind for the aircraft then  I guess it does not matter?

Oh come on, this question specifically asks if there is ever a case where aircraft are asked to taxi along to the other end due to a wind change. The other questions are about traffic flow in the air and whether you can takeoff/land downwind. Can we please reopen this?

Yes, I have seem a case like that while spotting at a airport. The aircraft simply entered the runway at taxi speed and leave at the next exit, back to the taxiway going to the other runway threshold. It was not exactly lined up already, but holding short of runway when that happened.

This is actually answered in the top answer to this question here: http://aviation.stackexchange.com/questions/9126/how-does-a-large-airport-switch-flow?lq=1

@JayCarr no, it describes the procedure to switch the runway direction, not if the conditions ever changed so fast they needed to taxi waiting aircraft to the other end.

There are a few major airports with single runways, however I'm guessing that the chances of the wind doing a 180° flip in a short period of time is small, usually they'd be able to get the waiting aircraft out with a cross-wind while setting up new departures for a more favorable runway.

On a flight few years back we even commenced the take-off roll, aborted at low speed and taxied to the other end due to wind change. Apparently the pilots originally planned take-off with slight tail-wind and got report the wind increased beyond the tail-wind limit at the last moment (LIMJ is not that big, so there was no queue of departing aircraft).

What you are describing does happen. The runway change is a major event at a big airport and it usually occurs once a day. This becomes a major transition because landing aircraft have to be switched to the other end. AND, areas served by a single approach control, the change has to be coordinated with the other airports. Note that lines of aircraft waiting to take off rarely occur unless the airport is very busy and has few runways.
Thus, the runway change generally occurs over time (half an hour).
If there is a sudden, unpredicted wind change, generally, aircraft that are already at the "wrong" end of the runway are allowed to continue using it if they are able to do so.
So yes, aircraft will on occasion have to move to the other end of the runway.
I have seen this more frequently at busy general aviation airports than at commercial airport.

This occasionally happens at London Heathrow.  The tailwind limit is 5kts and if the tailwind component is below that (from the East), aircraft will generally use the Westerly runways for noise reduction purposes. If the tailwind component rises above this and at 15:00 each day, operations are switched to the Easterlies.  If the wind change is sudden and stronger than forecast, then a runway change can catch some poor souls at the wrong end of the runway who are then redirected to the other end.

I think I was at what you describe as a "very busy with few runways" airport. Mumbai, India.

It can happen at big airports too if the runways are parallel, which is common at airline hubs. For instance, KDFW has 5 parallels, so when they all reverse at the same time, it's a big deal. Such parallels tend to be very long to accommodate high crosswinds or even tailwinds so they can avoid/delay such reversals.

This goes back a few years, but I was on a 727 departing LGA, and we had to abandon our position in the queue to taxi to the other end.  Everyone was all ready taking off with a tailwind but the aircraft weight and airline opspec would not permit us to launch.  We had to taxi to the other end but soon all the other planes joined us, because the wind was increasing over time.  Net result we took off sooner!  Happy dance!

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Would a 90 kg object jettisoned from an aircraft create a detectable movement?
I was reading the description of an old hijacking which has this snippet of interesting information:

After takeoff Cooper told Mucklow to join the rest of the crew in the
  cockpit and remain there with the door closed..... At
  approximately 8:00 pm a warning light flashed in the cockpit,
  indicating that the aft airstair apparatus had been activated.... The crew soon noticed a subjective change of air
  pressure, indicating that the aft door was open. At approximately 8:13
  pm the aircraft's tail section sustained a sudden upward movement,
  significant enough to require trimming to bring the plane back to
  level flight. At approximately 10:15 pm Scott and Rataczak landed
  the 727, with the aft airstair still deployed, at Reno Airport....an armed search quickly confirmed that he
  was gone.

Would a 90 kg man jumping off the aft stairs of a B-727 in flight create a detectable "sudden upward moment". Not just a slight one but "significant enough to require re-trimming"?
Doesn't sound like a fluke or the product of a vivid imagination because we further know that:

An experimental re-creation was conducted using the same aircraft
  hijacked by Cooper in the same flight configuration, piloted by Scott.
  FBI agents, pushing a 200-pound (91 kg) sled out of the open airstair,
  were able to reproduce the upward motion of the tail section described
  by the flight crew at 8:13 pm.

The full story is here:
https://en.wikipedia.org/wiki/D._B._Cooper
I'm estimating the mass of a fully-fueled B-727 as about 60,000 kg. A detectable perturbation by a 90 kg ejected body sounded a tad unlikely.
But I'd love to see a more accurate calculation. I suppose the center of gravity and the long lever arm for the aft stairs location will matter?
PS. It seems far more plausible to me that the movement detected was actually due to the aerodynamic forces on aft stairs and not the effect of the ejected 90 kg mass. The only reason I was rejecting this explanation was that the timing seems off if we are to believe the flight crew report:
They seem to have detected two events: A pressure change and later this reported sudden movement. So the movement does not seem correlated in time with the aft stair deployment.

In the EMB-145 you had to continually re-trim just from the flight attendant and galley cart moving the length of the cabin.  (normally transparently done by the autopilot but if you hand flew it at cruise you definitely noticed it).

@casey Interesting. Then again, the B-727 would be roughly 5x heavier than the EMB-145?

depending on model, max weight is in the 20,000 to 25,000 kg range. You'd also see a larger change in the 727 because the moment arm at the far aft airstairs is large.

Related question, but not duplicate: http://aviation.stackexchange.com/questions/24447/could-d-b-cooper-know-where-he-was-landing-when-he-parachuted

Yes
It's not just weight, it's also aerodynamics. First let's assume that the aircraft was trimmed slightly nose-heavy (no passengers), therefore it's trimmed slightly "tail down" anyway
When the stair was first opened, it would have been held partially closed by the airflow under the fuselage - it's not heavy enough alone to extend fully against a 100 knot wind.
There was then a two-part change from Cooper leaving the aircraft - one of him walking down the stair, pushing it into the airflow and acting much like the elevator.
When he then jumped, the loss of his weight at the very back of the aircraft, along with a presumed "push" against the door, pushing it further into the airstream, would have simultaneously jolted the tail up, then reduced the weight at the very back of the tail "lever".
90kg doesn't sound like very much, but when it's at the very, very back of quite a long lever, and when combined with the airstair, the results seem perfectly reasonable and, indeed, were proven by the FBI.

A tail at the end creates a pitch up moment. Therefore dropping that weight creates a pitch down moment. The door create a pitch down moment while deployed, so letting them partially close again would create a pitch up moment as described. But the weight itself does not contribute, it works against it.

I'm talking about the combination of walking down the stairs (pushing the door into the airstream) and then pushing off the door to jump out. Pushing the tail up momentarily, combined with the overall loss of his weight (over the course of a few seconds) from the tail. The weight change the trim, the door merely helped by pushing the tail up momentarily for a couple of seconds between the weight being there and then vanishing.

The weight in & of itself is utterly inconsequential. Having paratroopers walk off the ramp of a C-130 is unnoticeable on the controls. (Drop a Humvee -- you notice that!) Only the aerodynamic effects would give a pitching input the pilot would notice.

I would suggest that the aft stairs acted as a control surface lifting the tail. Perhaps they will not extend fully against the slipstream until a weight of 90 kg is applied to the end...

I had thought the same thing. And maybe you are right. I was only discarding that explanation because the description makes it seem that there was a delay between the flight crew detecting the stairway deployment (pressure change) and the actual jump (the movement).

I'm pretty sure that the 727 airstair acts as a tall stand to keep the plane from tipping from uneven loads. It doesn't just drop down from weight, it opens hydraulically

@TomMcW Thanks. In light of your comment, then the relevant question would be: How strong are the actuators in the context of what drag forces you would expect on the slide when opened during flight.

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Would building a large asphalt square or painted dark black area create a "thermal generator" for glider use?
Imagine if you build a "parking lot" square of asphalt and paint it the deepest black possible to absorb maximum heat...would that spot essentially be a thermal generator that you could fly over with a glider and reasonably expect good thermals? Assume it's summer and no other obvious obstructions to solar radiation on the day.
Even on a day when there's a relatively low altitude temperature inversion, could this make the air so hot that it would take a good vertical distance for the thermal generator's "parcel" of air to cool to the ambient temperature (and still make a flyable thermal above the normal inversion altitude)? Or, do thermodynamics not really allow you to get very far with this...assume usual 5.4 degrees Fahrenheit of cooling per thousand feet.

This question is not about aviation, should be asked in a physics forum.

I disagree...glider pilots and pilots in general apply physics all the time of course.

That does not make this an aviation question.

Unfortunately, while interesting, this question is not aviation specific. It would be better placed in the physics stack exchange as opposed to this one.

Wouldn't a perfectly glossy white surface perform better?

@CarloFelicione "that you could fly over with a glider and reasonably expect good thermals" does not appear to be a good fit for physics.

@slebetman You want a heat source on or near the ground. Reflecting your energy doesn't do that since once its reflected you don't have control over the direction it goes.

This is rather a tooic for the Earth Science SE (and boundary layer meteorology in particular). It of course belongs to Physics in general but is pretty specific and calls for specific experts.

@CarloFelicione the question was edited to better define the scope of the question to be aviation specific. The earlier comments exist prior to that change and were made in response to those comments. Chill out.

Glider planes are most definitely part of aviation. What propels and lifts them is also part of aviation. Voting to keep open.

Black tarmac parking lot (or solar farm, or...) does work. but it needs to be Large. Football field size is way too small. 0.5x0.5km works great.

Thanks everyone for the awesome comments and contributions!

Yes, if it was large enough you could expect decent thermals from it, but not all the time.  I've flown over mall parking lots where there is maybe 20 acres of asphalt, expecting a boomer, but no joy.  Thermal sources can be frustratingly unreliable.
On the other hand, at my glider club there is a nearby solar panel farm, with panels covering probably 30 acres.  It is actually a fairly reliable thermal source, seemingly better than a parking lot and I often head over to it when I get low and need to stay near the airport; I can usually expect at least some weak lift from it.
As far as paving goes, you get nearly as good thermals from dry dirt fields, so spending a million or two to pave 20 acres seems like quite a waste of money, especially when you really want to have thermal sources distributed all through the area you want to soar in.  Lots of farm fields with low moisture content and minimal vegetation cover will provide plenty of lift on a sunny day.
If there is an inversion capping the convection layer, it seems to inhibit all the thermal sources, and you won't find a "breakthrough" thermal coming from a parking lot.  Even smoke columns from large fires, much stronger than a typical thermal, tend to stop and spread out when they hit an inversion.

You need to add something that helps the warm air to get unstuck from the ground. Then a 20 acre parking lot would be generating great thermals.

The silicon of solar cells is a pretty good absorber of thermal radiation. Keeping panels cool to improve their efficiency is an issue, so spectrally-selective coatings can be used to reduce heat absorption, but the reflected heat then warms the ground near the panels - almost as good.  Then the panels are arrange a little like the fins on a heatsink so I would expect decent convection  in still air.  There's probably an optimal size for enough air to flow right in, and that will depend on the type of ground cover

@PeterKämpf  Not sure that's all of it.   Don't know for sure, but I've theorized that the thin asphalt layer with a thin insulating layer of gravel under it just doesn't have the thermal mass of a couple feet of continuous dry soil, so the asphalt surface tends to produce more frequent but smaller cycles compared to a dry field.  I'd always been disappointed with the results I got when searching for lift over parking lots.

If it has minimal vegetation cover it's not much of a farm field is it?

Any field right after harvest after a summer drought, or early season in spring after a dry winter, "brown" ones in other words, will give intense boomer thermals on a fair weather day with unstable air.   If the moisture content in the soil is high, it has a strong moderating and energy storage effect and the thermals will be weaker, but will continue later in the day.

@JohnK The moisture content will likely  have have larger impact on the Bowen ratio and the latent heat fluxes being present instead of the sensible heat fluxes rather than to the ground storage fluxes. But this effect surely exists as well.

@PeterKämpf What do you mean the help to get unstuck? There is plenty of turbulence in the surface layer in particular or in the whole convective boundary layer in general.

@VladimirF You'd be surprised how reluctant warm air is to separate from the ground when there is little wind. On a flat landscape, it sometimes drifts for kilometers with the summer breeze until a forest edge or even a passing truck will give it the needed kick.

I made a short LES simulation

The color is thhe potential temperature and the scale span is 1.8 K between blue and red. There is a hot patch 100 m x 100 m in the middle. There is 0.1 K.m/s (~110 W/m^2) sensible heat flux elsewhere but 0.3 K.m/s (~330 W/m^2) in the that square. The wind speed is very low, only 1 m/s (~2 knots), still any significant long-term stationary plume is hardly visible. The BL height is about 1 km (900 m at the start, but the gif starts later). The case is completely dry for simplicity. With 30 fps it is 2 minutes of real time per every second of the animation.
Even after 1 hour averaging, the increased temperature is only visible quite localized close to the ground and the vertical velocity field is just determined by those large convective cells, any rising current from the patch cannot be identified in the 1-hour-averaged vertical velocity field at all. Note that the closest point is 5 m from the ground so we do not see the extremely hot layer very close to the surface, but it is properly parametrized.
The 100 m x 100 m ("football field") patch was simply too small to have a significant effect. It will help you in the surface layer, and may get you from the winch altitude to some bigger thermals, but it certainly won't get you to the inversion. Or it will be good for soaring birds.
Those sensible heat fluxes I applied are not low but rather typical. Remember that normally a large part of the total heat flux is taken by the latent heat flux.

Firstly, please note that surface heterogeneity is not necessary for thermal convection. Convection happens because of the surface heat flux and thermodynamic instabilities, not because of heterogeneities. Heterogeneities may introduce secondary circulation and various currents.
According to the simplemost particle method, an air particle will raise roughly to the height where its temperature will equal the temperature of the surrounding atmosphere. Your 5.4 K per 1000 ft corresponds roughly to the dry adiabatic lapse rate, that means that the potential temperature is constant. That happens in the mixed part of the convective boundary layer and after the capping inversion with some step rise it will then increase with some gradient.  If you heat your thermal say 1 K above the mixed layer potential temperature, then it will rise until it equalizes with the surroundings. If your pot. t. gradient above the mixed layer is 1 K / 100 m, the inversion is weak, it may rise roughly another 100 m. 1 K is already a lot. It won't get you kilometers above the capping inversion. Only large convective clouds can do that.
Even regular thermals do enter the stably stratified layer above the capping inversion and cause entrainment. This is the entrainment layer.
The real thermodynamic temperature is less convenient because it decreases in the mixed layer (9.8 K per 1 km) and then may either increase or decrease above the capping inversion (end still be stably stratified, the sign is not that important).

Your simulation is very good.  Can you run it with no wind please.  You may get stronger thermals, but they will probably "mushroom" not too far above the "hot spot" (dry model), due to mixing with the surrounding air.

I have no idea whether this answer is right, but definitely "+1" for lots of thought and effort!

@RobertDiGiovanni I tried that. It took me some time to find free time and CPU time on the cluster. The difference is very small and it is even worse to see something in the results because the large convective structures tend to stay in one spot for a long time. Even after averaging for two hours I cannot see anything in the vertical velocity field, just the noise from the large structures. The average temperature field is very similar.

@VladimirF the last sentence of the extract says alot.  If we can ever get all the right information into the computer, it may turn out closer to what nature actually does.

Yes.  Sunlight is about 1000 W/m2.  Absorbing it is a good way to get some heat.
We can improve on your design a bit.  A good portion of sunlight is visible to the eye, but some of it is not.  Not all "black" materials will perform equally.  Pick a material that absorbs the invisible infrared and ultraviolet, too.  Choose a material that is thermally insulating (like asphalt or most soils) to increase the amount of heat that goes into the air.
If you heat the ground everywhere then you have no control over the location of your thermal.  Surround your dark area, which should probably be a circle rather than a square, with a white area.  This will help your thermal stay put when the wind is light.
Your dark area will be most effective (per unit area) when the sun is directly perpendicular to the surface, which only occurs in the tropics (for horizontal surfaces).
Reference: https://www.nrel.gov/grid/solar-resource/spectra-am1.5.html
https://en.wikipedia.org/wiki/Black_body

"How much sunlight does the ground absorb and reflect?" is an important question to the solar energy industry.  It turns out nobody's studied it in detail until very recently.

Radiation properties of natural surfaces and sensible and latent heat fluxes between thes surdaces and the atmosphere have been an important topic  in meteorology and climatology for decades.

Also, 1000 W/m^2 is way too much in normal locations (say, USA or Europe). 1000 W/m^2 will be only possible where at noon at latitudes where the sun is directly in zenith. So only once or twice a year between the tropics.

@VladimirF Standards organizations disagree with you.  https://www.pveducation.org/pvcdrom/appendices/standard-solar-spectra

Standards organizations do not determine what radiation  to the Earth's surface. Mother nature and physics do. And they agree with me. The Solar constant is measured above atmosphere and at a surface directly oriented towards the Sun. Those 1000 W/m^2 is what remains from those 1366 when it reaches the surface, but still  at a surface directly oriented towards the Sun. That (in USA those 900 because the path through the atmosphere is longer) may be relevant to solar panels that track the Sun, but it is irrelevant to normal terrain.

The question is not about normal terrain.

I've added a summary of your comments, but I feel that's too trivial to be necessary.

The question is about horizontal terrain (parking lot).

This may look trivial to you but this is how heat fluxes (including radiation fluxes) are defined. On a unit area of a given surface. If that surface is horizontal, such as a parking lot, than the irradiance or global radiation or whatever you want to call it is measured per unit area of that horizontal lot. And will be nowhere near those 1000 W/m^2 in mid latitudes.

@VladimirF See https://globalsolaratlas.info/map  Not everyone lives in mid-latitudes, and it turns out atmospheric moisture is far more important than latitude.

But that atlas is for solar energy. Those are oriented towards the sun. Parking lots aren't. The more northern you get, the bigger factor it adds. And the numbers are in intergrated kWh, it is quite tricky to recalculate those numbers to instantaneous maximum watts. This is a mistake even had to uncover in a paper I got for a review. They used these numbers as if they were W/m^2.

Yeah, Vladimir's comments are very accurate. 1,000 W/m^2 is approximately the maximum possible instantaneous solar energy density on Earth's surface, not a typical value. It happens essentially only near solar noon in or very near the tropics and, even then, only at certain times of year. Actual average values are typically a few hundred.

It would take more than a giant flat horizontal square.
This is not based on any numerical proofs but from my observations of weather in my area. I decided to add this answer after reading the discussion in the comments of Robert DiGiovanni and Vladimir F on Robert's answer about moisture and convection. To get a good strong thermal you are better off finding rather than building, but you may be able to enhance an existing location.
What you want is a large water area upwind probably 1-2 miles from steep (over 1:1 slope) hill and then place your thermal enhancement on the slope of the hill someplace below and not immediately before the crest. This should enhance the land breeze and the thermal energy will be concentrated in the area just at the crest.
If you download Vladimir F's graphic and look at it in a tool that stops the loop, you can see that at frame 200 and again at frame 300 convective plumes are generated that track downwind from about the 1/3 point to the 2/3 point . Individually they do not have enough energy to push though the boundary layer, although the one at 300 does make a strong attempt. I wonder if this simulation was allowed to run out to frame 2000 or more if there would be a greater convective progression, but I don't know the time equivalent scale of the frames to be sure.
The key is elevation change to impart an upward trend to the moist air mass and the additional thermal energy from a dense heat moment to accelerate moist air up through the boundary layer.
This is how clouds form downwind of Lake Erie in the summer. At the lake edge there are wind and solar farms, inland about 20 miles there are more wind farms on the taller hills. Convective cloud formation happens about 5-10 miles inland after the maximum 200NM fetch across the relatively shallow lake which late in the season can see water temperatures in the mid 70's.
Also if you are in the Northern Hemisphere, generally, a Low Pressure system  north and east of your location will increase airflow into a western facing slope, as will a High Pressure system south and West of it. These are reversed in the Southern Hemisphere.

I have no idea whether this answer is right, but definitely "+1" for lots of thought and effort!

If you added a thin layer of water over it, or some type of steam generator, you might have something there.
H2O has a molecular weight of only 18, whereas air, predominantly N2 (28) and O2 (32) is much heavier.  Steam has even been considered as a lifting gas!
It is humidity indeed that powers the strongest of thermals, found in thunderstorms, the builders of hurricanes. The ability of moist air to hold heat a bit longer allows it to continue rising in dryer air.

clue:  "moisture content...has a strong moderating and energy storage effect, and the thermals will be weaker, but present later in the day".

So, now we see how to really "unstick" a thermal, by bringing in cooler, dryer air from around the "generator" and allowing it to rise with moisture added. Water vapor content has the added benefit of being strongly absorbent of solar radiation in the IR range, literally acting as airborne "asphalt" to sustain the rising column.  Your design may then look like a giant bulls-eye, surrounded by a low heat absorbing surface.
A "circulation" of rising and sinking air is also helpful to create a sustained, strong local thermal, so right next to your square do create another one that will cool and dehumidify the air, making it as dense as possible.
Analysis of a plume from a propane burner (which has water vapor from combustion) vs an electric hotplate (dry heat) can be used to measure strength and height of thermals produced, which may lead to better modeling before full-scale production of a thermal square begins.  If you succeed in forming a cumulus cloud, you may be in business (just don't get carried away).

This is completely wrong. If they add water, they will get loads of evaporation and very low sensible heat flux. Water vapour is indeed lighter. However, so much heat will be spent at the phase change, that the effect on thermal convection will be the opposite. Buoyancy is governed by the  virtual potential flux. If you manage to lower to Bowen ratio to say 0.2, you will get, at standard conditions, only 23% of the buoyancy flux you would get at dry conditions.

What actually enhances thermal convection is the opposite process, vapour condensation, when clouds condense, release the latent heat. The water vapour can store huge amounts of heat. But it must be released by condensation. Then powerful storms can emerge.

Everyone can check my computation. My result is that the factor is (1+0.61*q) * (b/(1+b)) + cp/LE * 0.61 * T * 1/(1+b) where b is the Bowen ration, q is the specific humidity, cp is the specific heat of air, LE is the latent heat of vapourization and T is the temperature.

@VladimirF  That's why you wait awhile for the water to heat up.  But there is another way of doing it.  Vegetation around the square will provide cool, moist air.  This will be your "sea breeze".  The important thing is circulation.  Thunderstorms have an extra "kick" by forming clouds and wringing out the moisture, so now one has a cool, dry downdraft.

No, you don't understand. Any water you add to the surface, no matter if from vegetation or from water surface, will stop your convection. Will rob you of your buoyancy.  Instead of the energy going into the motion of the air, it will be stored in the water vapour and only released in some thunderstorm thousands of miles away. Yes, the water vapour is somewhat lighter. But you lost too much heat to get it there. It will get you much more buoyancy to heat the air to higher temperature. It is easy to calculate by how much.

And if you already have the air moist around you,  in a surrounding vegetation, than you also don't get much. Well you get, you get the bonus for keeping your parking lot dry. But that is the opposite to what you suggested in your answer. You need everything around you wet, so that the air stays cool, and your parking lot dry, so that the air there becomes very hot.

@VladimirF it does not seem right or wrong, just 2 ways of making a thermal.  The forest is cooler due to transpiration.  You may be underestimating the contributing factor of water vapor to bouyancy and lower cooling rate and (if it condenses) further updraft.  Simply warming the lot will rise the air, but a will rapidly cool into surrounding air.  Adding water to the lot will cool it, but with continued energy absorption...

Well, I am definitely not underestimating the contributing factor of water vapour to buoyancy. That factor is that 0.61q and 0.61 in front of the other term. 0.61 being the ratio of the gas constants, respectively the inverse ratio of molecular masses of H20 and of the dry air. This contribution cannot overcome the heat you need to use to use for evaporation. This heat will then be missing from your thermals. Yes, part of it will be released when the air condenses, but most will get released somewhere far.

Specifically, the buoyancy flux is g/T (1+.61 q) w'T' + 0.61 * T * w'q' in terms of the kinematic fluxes. The kinematic fluxes are related to fluxes in W/m^2 as Qh= rho * cp * w'T' and Qe = rho * Le * w'q'. The latent heat flux Qe happens at the expense of the sensible heat flux Qh.

@VladimirF. OK, the water holds heat longer and is lighter: the thermal is sustained.  Air by itself is actually a pretty good insulator and does not hold heat well.  For now, I'll be patient and put my bet on the hurricane,  but thanks for some excellent thoughts.

authors: Vladimir F Героям слава


text:
which is better for stability between the delta and rectangular wing designs?
building a minuscule version of an airplane and need to know between delta and rectangular designs which would be better. I don't need any other designs, just delta and rectangular. Tailless. Which adds more lateral stability

Tail-less?  Would make a difference.

Not enough information

In an aircraft with no horizontal stabilizer, it's much easier to create a design with adequate pitch stability if the design has a delta wing than if the design has a rectangular wing.  If the design also has no vertical stabilizer, the advantage of a delta wing over a rectangular wing is even stronger.
If you go for a rectangular wing in either of these cases, you'll find that the CG position is extremely critical.
Here's one website with lots of images of tail-less hang gliders, including early "Rogallo" designs which were simple delta wings.
Your question has been modified to say that you are interested in lateral stability-- an aircraft's tendency to resist rolling away from wings-level.  Delta wings and swept wings contribute a dihedral-like effect that contributes to lateral stability even if the wing has no actual dihedral.  If you want to create lateral stability with a rectangular wing, you'll have to give the wing actual dihedral, or you'll have to mount it well above the CG.

(Of course, the hang-gliding paradigm opens up the "pendulum stability" can of worms again... )


text:
Is needing to urinate an emergency?
I'm planning a 3.5 hour trip. Usually I urinate more frequently than that, but I will not drink many fluids the morning of the flight in an attempt to get to my destination directly.
If a pilot or passenger cannot hold it in any longer and the only nearby airport is controlled or military, is it grounds to declare an emergency?
After all, holding it in for too long is a risk to life. See KDND radio station "Hold Your Wee for a Wii" contest.

You just call (bed)pan, (bed)pan, (bed)pan. badum, tsk!

There may be a risk to the cabin upholstery, but as long as the aircraft's electronics and other vital equipment are not in danger I don't think this would be considered an actual emergency.  But as indicated in the answer that you received you may find some sympathetic controllers who will help you out. Just don't ask for them to roll the emergency vehicles.

You have options

You can use one of these.

We had a phrase in ATC, "Poor planning on your part does not constitute an emergency on my part." Planning a trip longer than the length of your bodily duration seems unwise. I don't think regulators would think it was justification for landing at an airfield that would otherwise be unavailable to you.

If you are male this can very easily be solved with a bottle.

@RetiredATC I don't like that saying at all. Many accidents are caused by poor planning. Pilots shouldn't be afraid of declaring an emergency out of embarassment- if they're in an emergency situation, declare an emergency and worry about blame later. (Mind you I don't think having to pee is an emergency in essentially any reasonable situation).

The "risk to life" requires drinking a large amount of water. I'm not a doctor, but I doubt it would happen if you don't drink much and have to hold it in for a half hour. I think you're much more at risk of wetting yourself because you can't hold it in.

If you feel 3.5 hours is going to be too long, why plan that as a single flight? From the planning phase, incorporate a stop around midway (or more, if needed).

Just use a "Travel Urinal". Or if you must, you can also use a diaper. If it's a 4-seater or a 2-seater I'd just use a diaper. People have incontinence too, who cares, people don't even have to know about it, etc.

In my mind, "emergency" means serious bodily injury, serious property damage, or serious loss of money.  I don't think wetting yourself counts as any of those.

This question is a health/medical question, not an aviation question. 3,5 h is way too low for a healthy adult if you just drink water (no sugar, caffeine, alcohol etc).

@d-b completely disagree on both accounts

@Cloud You should see a doctor, you have health problems.

Is needing to Pee an emergency?  Depends!

@RetiredATC: ...and if you have to pee unexpectedly-soon after your previous pee?

Oh boy has this very nearly happened to me. 3 hour flight and about 1.5 hours in I started to feel the need. I managed to make it to my destination, but I have never sprinted so fast from the apron to the clubhouse.
You're the pilot in command. If you think it’s an emergency, then guess what it is?! I'm not sure we're in mayday territory here, but my comment was half tongue-in-cheek; a pan call could well be justifiable. If nothing else, it'll get you number one in the circuit and on the ground faster.
In the UK at least, you're rarely that far from a suitable airfield. Controlled is not a problem (except Major London ones—unless you have very deep pockets!), military may be—avoid if at all possible. Divert to the nearest suitable airfield, get on the radio, tell them you have a bladder-based emergency and they'll get you in ASAP. Believe me, you won’t be the first. It happens all the time.
Oh, and don't dehydrate yourself too much—that's probably worse for you than holding in a wee for an hour.

"it'll get you number one in the circuit" - especially if you're passing (over a body of) water

Is it really appropriate to refer to this kind of call of nature as a "pan call"?

I can't help but rudely mention that a packet of high-quality absorbable underwear is ~£20, will hold the entire contents of your bladder remarkably effectively, and not require you to do anything if you're caught short. I know this because I had a spinal injury and had to discover the hard way what it's like to use them. It's really, really not that bad at all.

Since most adults don't wear diapers, most people probably don't follow advancement of diaper technologies. It is absolutely nothing like a wet rag against you. Properly made diapers will wick away the moisture from your body to prevent rashes. Ladies will have a little bit more familiarity with sanitary pads.

Arriving at your destination with wet trousers/skirt is certainly no one's desire, but I don't think that can be called an emergency.  Worse comes to worse, you let loose and let the fabric absorb your urine.
Now, if that will potentially disable the aircraft, then it is certainly an emergency.  But that's also probably an aircraft that shouldn't be aloft,  because that means simply spilling a beverage could bring that plane down.
One thing to consider is that another aircraft may be experiencing a life or death emergency (more serious than wet clothing), and so your situation may receive a lower priority. And given that most ATC traffic is recorded and accessible to the public, the "I really need to wee!" emergency call will undoubtedly get a lot of attention on the interwebs.
My recommendation?  Simply buy some adult diapers.  They don't cost more than a few liters of aircraft petrol, and will hide any accidental spillage.  Plus, they are extra cushy for your tushy, so they make uncomfortable aircraft seats more comfortable.  Or so I've been told (ahem).
Or you can get a contraption that fits your man/lady parts and deposits the urine in a baggie.  But do you really want to have to explain that contraption to security?
BTW, we've all been in the situation in which we suddenly need to wee.  And as humans age, it typically gets worse.  And some diseases make it much worse regardless of age.  So ATC may be accommodating if you explain the situation and ask nicely for a priority approach.
Finally, as a pilot or a passenger, anticipating one's bodily functions is important.  Few (none?) of us can do it perfectly.  But keeping logs (ugh, no pun intended) ahead of your trip of what you consume, your medications, the temperature, the humidity, and how it all affects your output can really pay off.  Hydration is important, but too much hydration can lead to significant discomfort.  I learned this lesson the hard way by trying to watch Lord of the Rings in the center of packed movie theatre while drinking an extra large green tea smoothie.  I'm normally a very respectful person, but I expected security to remove me from the building because I think I knocked over several people racing to the loo after that 3 hour horror film.  It wasn't until afterwards that I learned green tea is a diuretic.  My bad, and my apologies to you 22 years later if I toppled any of you over in that theatre while yelling "Make a hole!" on the top of my lungs.

"Or you can get a contraption that fits your man/lady parts and deposits the urine in a baggie. But do you really want to have to explain that contraption to security?" - Or just stash an empty bottle in your flight bag to pee into if needed.

You are the Pilot in Command. You decide whether something is an emergency or not. Keeping in mind that the threshold is whether the safety of the flight is in question, not the comfort.
If you feel that peeing your pants would cause you to immediately lose control of the plane, then it's an emergency. If, more realistically, you feel it would make you feel gross until you have a shower and get a change of clothes, then it's not. I doubt the FAA or military would agree if you choose the former, so you may have a bad time of it. But that is, of course, better than crashing the plane.
If you're planning a 3.5 hour flight, you should have diversions in mind anyway, in case weather or other circumstances make continuing your flight risky. Be ready to divert to one of these if/when your bladder informs you that making your destination is impossible.

No.
Pilots can declare an emergency in situations when they believe the safety of the flight is compromised.  But needing to use the bathroom is generally not considered a valid reason to declare an emergency.  Pilots are expected to plan for such basic human needs as part of their pre-flight preparations.  Such plans may include avoiding excessive fluid consumption, using the facilities before departure, filing a flight plan with more stops, or even utilizing a bladder relief device.
The declaration of an emergency in aviation is a serious matter that triggers a significant response from air traffic control, emergency services, and other authorities.  Pilots are generally expected to use the term "emergency" when there is a significant threat to the safety of the flight or those on board.

"Pilots are expected to plan for [whatever] as part of their pre-flight preparations." Failing to plan for something that you should have planned for doesn't prevent something from being an emergency.

What if you were hungry. I can hear the pilot appealing the one-year suspension saying, "But your honor, I was really hungry and didn't bring any snacks. Hypoglycemia is a real thing, so I landed at Edward's AFB hoping to go to the O-Club to get some eats."

@RetiredATC Especially for a diabetic hypoglycemia is a very real thing and the situation can be a very real emergency  with a very real risk of the pilot passing out. Now, I don't claim that the pilot won't phase consequences while on the ground and I do not know whether such a diabetic can get the required medical class. But in the air it can be a very real emergency, not dissimilar to a pilot who forgot to fill the fuel tanks.

@Vladimir Of course I know hypoglycemia is a real thing. It was tongue-in-cheek. We had diabetics working as controllers, but their diabetes had to be very tightly controlled with numerous regular blood sugar tests that were documented for the flight surgeon's review. I'm not sure what level (third, second, or first class) pilot's medical certificate such a person could obtain in the US.

You will have a hard time winning the argument that the need to deviate your flight plan is a true emergency if it was reasonably foreseeable.
In short, faking an emergency is a BAD IDEA!  Don’t do it.

Whether something is "reasonably foreseeable" has nothing to do with whether it is an emergency. If you are in an emergency situation, declare an emergency and worry about who was responsible for the development of the emergency situation and what you could have done better once you're safely on the ground.

authors: Vladimir F Героям слава


text:
Why does a fuel-injected engine have a mixture control?
For example, in a C172S fuel injected type, what does the mixture control lever control exactly in the fuel system?
They have a fuel air control unit which regulates fuel flow based on air passing through butterfly valve.
Then what exactly does the mixture lever control?
I guess the fuel air control unit works to maintain e.g. 15:1 fuel air ratio and the mixture control lever selects the ratio? Like if I lean the mixture lever, would the fuel air control unit now try to make a 16:1 ratio?

Basically two reasons:

You want to use richer mixture for climb as the engine would otherwise easily overheat during slow flight at high power without the excess fuel providing extra cooling. And leaner mixture for cruise for better economy.

The fuel control unit is fairly dumb—to keep it simple—so it does not compensate for air density perfectly and some fine-tuning is still needed.

A FADEC (full-authority digital engine computer) equipped engine could automate both functions, and automotive engines do, but this is an old design without electronic control that they didn't want to update much, because it would be very expensive to ensure the reliability required of aviation engines for the new components.

The throttle butterfly varies the volume of air that enters the engine, but fuel-air mixture is a function of weight of air (and fuel).  The control unit doesn't sense weight of incoming air.


text:
How to calculate time-of-arrival of airplanes to a neighborhood of a position (with minimum probing)?
Suppose we have a position on earth with coordinates: (latitude, longitude). I'm looking for methods, algorithms or APIs to get a time alert that a plane would fly overhead in the neighborhood of that position. What are my options? Here are my thoughts:

Use a web-based API to query all planes in the interest bound, periodically.

Downside:  For average speed of airplanes (1000km/h), for a 1 degree in variation in latitude/longitude (approx. 100km), we have to probe the API every 6 minutes so not to miss the overhead plane. For a 0.1° variation (~10km) which fits the "flying overhead" description more accurately, this probing period is 36 seconds which is too much of a burden on both the machine and endpoint server.
This does not give us a "time-of-arrival" per se. It just continuously checks for overhead flights.

To solve the frequent probing issue, first, use the API to query for flights in a bound much larger than interest bound. Then for all matched flights, only choose those whose predicted route passes over the interest region. This method gives us time-of-arrival.

Downside: How can we "predict" a flight route? We can use "dead-reckoning" meaning we assume a fixed heading, then predict the time of arrival of the plane in the interest region according to its initial speed. But problem is, planes may change their heading arbitrarily. So we may miss some planes who were not even in the first probing phase to begin with, or we may have false positives for planes which change their route after our probing.

Use some fixed predefined flight route API.
a)I don't know of any such APIs that provides routes or waypoints.
b) The timing may be well off due to frequent delays in the industry.

These are all solutions I could come up with. Any ideas?

This is too broad.  You need to provide the kinds of data you have available and some performance parameters/metrics.  How far ahead do you need to know.  How accurate do you need to be? How much compute power do you have available? What information about a flight is provided by your API?  Destination?

@Jim I'm ok with 30 minutes or 1 hour scan period for flights in any bounds (so a 0.5/1 hour early alert. ) Consider the neighborhood to be within 0.1° latitude/longitude of observer position. Compute power is typical modern PC (it's not an issue) but too frequent calls on API is not desirable.
Flight heading, elevation, speed, lat/long, ICAO identifier.
Any origin and any destination.

Is this for any flight including ad hoc GA private VFR flights or for scheduled commercial service only?

This is more about programming, algorithms, and an API than it is about aviation. VTC as too broad, though off-topic also applies.

Have you heard of Flightaware.com?  If not, check it out.  If so, maybe you could help us understand the actual end goal or problem at the root of this?  (assuming this relates to your other question?)  I mention it because perhaps there is a simpler way to address your actual objective...

@MichaelHall Yeah. It provides flights currently present in a location. But I want a timestamp for all future flights that pass over the neighborhood of a location.

@Jim Mainly what flightradar24 shows. But I'm ok with limiting the scope to scheduled commercials.

You'll also have to allow for the winds aloft, they are going to vary in speed and direction by altitude.

I don't think there's any "easy" way to do this, but your best bet is probably to create a data table of flights linking city pairs served by scheduled commercial carriers that may cross your region.  This could be done using flight planning software, including free web based such as Skyvector, or the old fashioned way with a paper chart and plotter.
Draw a radius, (or square) around your location of interest, and count how many flights cross the area you have determined the size of from your other question here:  Hearing plane overhead
Then look up departure and arrival times of all the airlines serving the city pairs you've identified as crossing your region of interest.  Enter the flight times in your table, and based on time/distance, calculate the point at which they enter and exit your designated area.  From this information you can make a column that will show that local time based on scheduled departures.
If you are computer savvy and want to automate things, write a program that will sample web info for posted departure delays and have your table updated automatically.  Then have the entry and exit times you've calculated "ping" your computer to alert you so you can go outside and listen.
I can't offer a suggestion on how to accomplish that last part because it is about computer applications, and not aviation.
Anyway, without more information on your actual location or the desired outcome you seek you probably won't get much more than the answer I'm offering...


text:
Does the stream of engine thrust act as a good drag shield against the nacelle?
Taking a look at the typical large engine of a commercial plane, it looks rather unstreamligned. Nacelle drag is significant IIRC.
However, then I suddenly remembered these engines produce a large jet of thrust (most of the time). Does this air stream of thrust act as a good shield against nacelle drag? Does it effectively form a bell cone, or half of a seers-haak body, around the rear half of the nacelle?
If so, that would appear to cut the nacelle drag in half.

The nacelle is not some solid block. For the flow it looks like a hollow, slightly blocked tube.
The flow ahead of the nacelle is indeed slowed down in flight, but only a little, entering the intake face at a flow speed of around Mach 0.4 to 0.5. This compresses the air ahead of the nacelle when flying in cruise at around Mach 0.8, so what enters the intake is already slightly compressed. Note that this compression does not involve boundary layers or shocks, so it is very efficient. The effect of the compression is that some of the air flowing towards the nacelle is pressed aside to flow around it. To avoid flow separation, the intake lip is rounded.
Pre-compression helps, because it raises the pressure in the whole engine and increases its thrust. What might be looked at as drag is in fact increasing the thrust of the engine! Of course, by further compressing and heating the ingested air the engine accelerates it, so the outflow speed of the core flow is easily double its entry speed. The outflow fills up the cross section of the engine, so the outer flow never has to flow into a void and experience separation (which is responsible for most of the drag of blunt bodies). Instead, it meets a faster jet of air once it has passed the engine fairing and is accelerated during the mixing process.
Only if the engine is idling or off will the nacelle cause real drag.

Great answer! Also, greater air mass entering the nacelle leads to even more bypass air, improving both thrust and efficiency.

That third paragraph really helps. Just for the record, it was form drag I was concerned with, not skin-friction drag. I suppose another way of asking the question is, If the engine was throttled back to produce a jet exhaust equal to airspeed (so incoming airspeed = outgoing jet air speed), would nacelle drag be greatly reduced?

@DrZ214: No, it would slightly increase. Most of nacelle drag is caused by friction, and throttling the engine will increase spill drag a bit and accelerate the flow at the end of the nacelle less, increasing the risk of flow separation. To be more precise, we need to clearly define what counts as nacelle drag and what counts as net thrust.


text:
Which types of aircraft need a gust lock? Is there a size / performance influence?
Which aircraft require gust locks on control surfaces?  Is there a certain range in the middle in terms of size / performance where gust locks (external / internal) are required?
From a cursory analysis is looks like the smaller / larger aircraft do not seem to have gust locks?Is there a certain tradeoff in size where they become required?
Does it depend on the type of actuators used for the control surfaces (e.g. hydraulic etc.)

Hydraulically driven surfaces generally don't require gust locks because the damping action of the actuator(s) is sufficient.
Non-hydraulic surfaces, that can be freely be blown around by the wind, generally do (an exception is something like a manual rudder that is linked into a nosewheel steering mechanism that inhibits free movement of the rudder on the ground - you don't need a gust lock on that).
This is either a mechanical locking system incorporated into the control linkage (best option as long as the mechanism is designed to make it impossible to take off with the mechanism engaged), or external locks installed after flight (not optimal, because you depend on the flight crew to confirm they are removed, and people screw up), or barring that, the old seat belt around the control column trick you typically use on light aircraft without a dedicated gust lock.
Bottom line is, regardless of the size of airplane, if the surfaces can be blown around and bang on their limit stops on the ground, you have to do something, even if it's just a seatbelt around the stick.

This implies the highest risk is on the “fly-by-fly” systems where the control surfaces are free floating and you control servo tabs, because there the yoke still moves even if the gust lock is engaged.

The Britannia had hydraulically operated control locks but I'm not sure exactly how they worked.  On the Dehavilland Canada products, the lock is always designed with an operating lever that blocks throttle movement out of idle when engaged, precluding flight with them on, and I think most airplanes with remotely operated locks do something along those lines.


text:
Heaviest Boeing vs Airbus aircraft: Why large (150 ton) difference in Weights?
An aircraft tug manufacturer's website had this interesting table:

Just curious, why the heaviest Airbus is a good 150 tons heavier than the heaviest Boeing? Otherwise, these two rivals have close competing aircraft for most specs.
I mean, how do the rivals end up with such different operating points. Obviously, I don't mean its an apples to apples comparison (different payloads) but what I mean is whatever market segment it was that Airbus was trying to serve with an A380, did Boeing not find that an interesting segment? Is this a strategic difference in a large plane / smaller plane sense?

Short Answer:
Difference in corporate mindset between the two companies and incompatible interpretation of market conditions and projections of future market demand.
Long Answer:
@Anilv answers your question to an extent but you should really understand the total scope of the commercial aviation sector. Airbus is a relatively newer company that has a widely different mission goal than Boeing: Airbus is an exclusively EUROPEAN owned multinational company with a majority share under EADS, the European Aeronautic Defence and Space Company. It was primarily brought together to give Europe and its smaller more specialized companies another chance against massive, government backed corporations from America (the big three: McDonnell Douglas, Lockheed Martin, and our big daddy Boeing). This actually caused quite a bit of a political sh*tstorm, with Boeing complaining that Europe's explicit backing of this new Airbus being far too pointed in corporate tie-in with government, but besides for some concessions made to ease relations with America, Airbus was allowed to continue receiving grants and other national backing from its parent countries.
Now to explain specifically why Airbus doesn't compete directly ALL the time with Boeing's aircraft is because frankly, leadership of both companies cuts projects all the time in different sectors because of their individual personas and visage for the companies' futures. I'm glad you mentioned the A380 because except for a few other situations continuing the A3XX (in-house title for A380 prototype) was by and large the most controversial internal decision made by any Airbus executive. The situation was this: Both Boeing and Airbus were looking at the VLA (Very Large Aircraft) concept, an idea becoming popular in the 90's due to burgeoning flight routes and demand for efficient carriers of mass amounts of passengers. Also, as the Gulf War ended Airbus had begun to reap profits with their A330 and A340 series aircraft. However, not too long ago Boeing had released its jumbo-jet 747-100 and -200, which were extremely popular and Airbus leadership was getting worried about their potential loss in this possibly goldmine niche. Alan Boyd, at the time president of Airbus North America reported after a joint study with Boeing of the market that Airbus predicted a market for about 500 to 600 airplanes, while Boeing envisioned a market for only 300 to 350. Interestingly both saw a profit margin of about $15 billion. Boeing saw the risk/reward too high, and at the time (I would argue it still is) was very encumbered with bureaucracy and promises to keep to the American government. It was a large project no matter what, and Boeing to an extent was on America's payroll after all. However, although risks were high for Airbus as well, the company exec at the time, the legendary Jean Pierson saw that the risk was worth taking, not only because of projected efficiency and prototype designs, but also because he needed to protect the rest of Airbus' lineup.
To even comprehend the complexity of the issues facing these men, you MUST understand that decisions to make or scrap a new plane isn't an isolated choice: an airline buying a new plane from one maker is highly unlikely to mix and match to buy a different size plane from another maker just to fit a smaller or larger route i.e. buy the A380 for its long-haul high-demand routes and the 787 for its longer but lower-demand routes. Boeing on the other hand had a relatively fleshed-out spread of planes and due to a HIGHLY incorrect mindset of complacency and EVOlution rather than REVOlution, they did not seize this oppurtunity to expand and improve. This was common knowledge to all business-minded men in the sector who were worth their jumping beans (sadly few at Boeing after , so the most prominent factor in Pierson's mind was probably his defense of the also-new A340 series, a small long-haul aircraft that fills a similar role to the new 787. This, as the chart you provided shows, filled a spot that was projected to be VERY profitable (as Boeing found out too late and rushed in the 787 to fill) but at immediate time was a little too hard to swallow for most medium sized airlines. Keep in mind that Airbus was still trying to prove itself to the world.
So, by Pierson's logic introducing a superior 747 in the form of the A380 would not only draw attention to the plane itself, but also help establish the A340 and start the ball rolling for future development of the wide-body long range medium size airliner. So, that's pretty much why the A380 was a (mostly) no-brainer for the Airbus group, and from the late 80's on, why Boeing and Airbus' line of airliners has considerably diverged. Hope this answers your question, and if you'd like more information or just clarification feel free to comment.
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The book Boeing Versus Airbus: The Inside Story of the Greatest International Competition In Business gives a wonderful account of everything I just detailed and more. I've read it multiple times and I never cease to learn something new from something under 300 words. Give it a try if you have time!

I'm not sure if I'd call the A380 a "no-brainer." Note that the book you cite is of 2008 vintage, and the last ten years have seen a different story. The A340 went away after only 377 built. And most people opine that the A380 and 747-8 are both at the end of their lines. I don't believe the A380 ever became a profitable endeavor.

You have a solid point, but like I said earlier its other purpose was to bring attention to its other line up. I'm mainly a proponent of Boeing personally, and you can tell I'm quite disappointed with their corporate half right now, but both companies make these decisions looking to the future. I may be wrong, but each company has future planes in the workings, so the A380 at this point should probably be seen as a hopeful stepping stone. Large planes are cool though, so the 'luxury' and novelty factor was kind of nice.

@TomMcW Any newer books that cover this subject?

@curious_cat I don't know. Even though it's from 2008 I'm curious to check out the one Jihyun mentioned

The French side of Airbus was green with envy when Boeing reaped monopoly profits from their 747 and subsidized the direct competition to the A300 and A310. Therefore, they became determined to put themselves into Boeing's position and have the biggest aircraft around. All studies after that were done only to rationalize that desire.

Is that your personal analysis or is there data to back that up?

@PeterKämpf Thanks! Can you elaborate more? In your personal opinion, had the envy been not there what would make sense as a rational sized aircraft in hindsight for Airbus? Not a 550 ton behemoth? What's your reading of the market dynamics?

@PeterKämpf You should post a full long answer on this topic in your usual encyclopedic style! I'm always curious to have your deep perspective. :)

Yes please do. I respect your opinion, but from multiple sources, including personal autobiographies I have read from some of these Boeing/Airbus execs contradict your claims about Airbus being jealous of Boeing for their profits. In fact, some make claims of the opposite.

Keep in mind the A380 is a larger aircraft that can carry more people than the 747-8, which may explain some of the heavier weight. In a 3 class configuration, the A380 can seat 525 passengers, while the 747-8 in a 3 class configuration can carry 468 passengers.
When comparing Boeing and Airbus aircraft of similar size, the weights are roughly equivalent.
As for the 747... considering that it was originally designed in the mid 1960's, it has held up quite well. But, it's days are clearly numbered.
One reason that the 747 (and A340) are headed for obsolescence and A380 sales are flat, is the cost efficient large twin engine airliners, like the 777, 787, A330, and A350.
To establish a perspective, consider that the A380 program began around 1990. At that time, the big wide body twins weren't in operation, and the general consensus in the aircraft industry was that large airliners had four engines. The first wide body twin, the Boeing 777, entered service in 1995, and its operating efficiency wasn't really seen until the late 1990's, when A380 development was well under way.
Also, ETOPS certification had only been issued to twin engine airliners in 1988, (the A320 being one of the first to get the certification) meaning they were now certified for long distance over ocean flights. The changes that brought on (among many others, the demise of the triple wide bodies like the MD11 and L1011, whose third engine was added only to get over ocean certification) weren't obvious in 1990.
In the interim, the wide body twins have proven to be extremely cost efficient... to the point where one can operate two 787's for slightly less than one A380, while carrying the same number of passengers and having increased flexibility. In operation, the A380 needs to be nearly full to turn a profit... so being able to use two big twins instead gives the airline the option to simply drop one flight if passenger load is light, and save a bundle. Another advantage is being able to fly smaller groups of people directly to smaller airports, while the huge size of the A380 tends to confine it to major hub airports.
One bet that Airbus made with the A380, being able to move a large number of people with a single berth and single takeoff/landing cycle at a major hub airport to alleviate airport overcrowding (with aircraft, not people), hasn't panned out.
I suspect a bit of hubris might have played a role, however minor. Airbus had lived in the shadow of the giant 747 for decades. Building something larger probably involved some pride. Not a major factor, but pride in having the largest might have made the profitability forecasts appear a bit rosier than they actually were. Yes, the aircraft industry is definitely male dominated.
Is Boeing more astute? Not all of their decisions have worked out. They (and the US government) spent a fortune on the 2707 supersonic transport, before abandoning it. It is likely that Boeing will take a 1 billion dollar write-off on the 747-8 due to poor sales (only 51 were delivered for passenger service), though that pales in comparison to the 25 billion Airbus spent (and probably will never recover) on the A380. Boeing ditched the 757, not long before that size aircraft became very popular (the A320 filled the need, and picked up a lot of sales). Their performance in the Joint Strike Fighter competition in 2000 (that produced the F35) wasn't so good, the delta wing design proved unsuitable for carrier operations. And, the airliner Boeing proposed when the A380 was announced, the beautiful Sonic Cruiser with it's high speed (Mach .98), was stillborn when airlines expressed a preference for lower operating cost over higher speed.
This article suggests that the Sonic Cruiser might have simply been a red herring... not sure how accurate that is, but it does make for interesting reading.
It is unfortunate for Airbus that the big twin airliner put the four engine airliner in general on the road to obsolescence, after they had invested a fortune in the development of the A380.
But, absent hindsight, that may not have been obvious in the early 1990's.

You may want to tweak the sentence, "The first wide body twin, the Boeing 777..." since the A300 was actually the first wide body twin, albeit not as large as the 777.

From a technical aspect.. the A380 was a fresh design to fit a wider mission profile. The B747-8 had to make do with an updated platform.
Stategically.. Boeing saw the future in more point-to-point routes rather than the hub and spoke system used by most airlines at the time. Who is correct? Well the A380 sold ok but those airlines that need them already have them and the growth of the market is pretty flat. Whereas the demand for aircraft like the 787 and A350 will only expand as demand increases.

They are both suited for hub and spoke networks, Boeing only believes that you should increase frequency instead of capacity on a given flight leg. This is possible on most OD-pairs, but a few European airports have run out of slots so they only way to increase capacity to that airport is to increase the size of the aircraft as there are no slots available for an increase in frequency.


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White light illuminating the engine coming on at intervals in flight; Curious what's the protocol?
I was recently flying Air China from Beijing to Bombay & happened to seat on the Window seat close to the wings.
I could see the engines and there was a light that could illuminate the engines. As I recall it was switched on at some point at the end of taxi and pre takeoff but I don't remember exactly.
What I do remember is that at some points during flight I saw the engine illuminated by this light and at other points (pretty much most of the flight duration) the light was off.
Just curious what the protocol was.
The aircraft type seems to be Airbus A330-300.
https://uk.flightaware.com/live/flight/CCA889
This was a neutral color steady light and not one of the red / blue ones nor the strobe. From the color it looked more like LED illumination.
PS. From the related question on SE Aviation the responsible light seems to be what they call a "Wing light". But my question is different than that one because why would the flight crew turn on the wing light during cruise altitude flight periodically?
There was no crew in the cabin for a damage / ice inspection (I've seen them use wing lights for this purpose post a deicing spray but then the flight crew comes into the cabin to look )

Do you know which aircraft type it was?

Possible duplicate of What is the diffference between landing lights, taxi lights and external lights?

Sounds like a logo light, perhaps.

@levu It was an Airbus A330-300. I've edited my question to add more details.

Maybe an ice inspection light?

The answer is in this post at the very bottom.  In the US these wing lights are usually switched on to make the planes more visible during takeoff and landings despite the fact that the lights are designed for ice inspection.  I don't know if China has the same protocols or not but from what you described it sounds like they do.


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Unmanned Drone vs Conventional Manned Fighter in Combat: How realistic?
How far are we / Is it even viable to think of a scenario where a drone gets employed to counter a conventional manned fighter?
I can see several benefits:

Free of the G-restrictions of a human the drone is free to undergo far more severe manouveres
Cheaper testing costs since a drone crash isn't as expensive / as unpalatable as the death of a test pilot
More risk appetite during actual combat since a human life is not at stake
The removal of the cockpit and life support / protective systems (e.g. No O2 tanks / No pressurization / No ejector seats) leading to a weight reduction, performance improvement and design flexibility. Perhaps allowing greater munitions loads etc.
The possibility of undertaking some version of suicidal yet mutually destructive manouveres that are out of question in conventional dogfights.

On the other hand, several limitations I can think of:

Poorer field of vision & situational awareness of a remote drone operator operating via cameras and sensors
The lag between control and reaction inherent to today's drone remote operator systems. Though how much of this could be improved via better technology is a crucial question. The current generation seems to use Ku band satellite signals. Could some form of ground network (but beyond enemy reach) provide more responsive controls? How close have we approached the fundamental physics latency limits even with existing satellite transmission technology.

As a totally different alternative, is the possibility of an unmanned, autonomous drone realistic? How far are we on the AI / sensors side where a autonomous decision engine can realistically be a good match for a human adversary in a dogfight. The autonomous option would make the control lag issue redundant.  (Redacted to focus the question on manned drones)

As this stands it seems way too broad and might venture into opinion. Maybe this could be separated into two questions of "advantages/disadvantages of UCAV vs. manned fighter" and "what technology is available/needed for a totally autonomous UCAV fighter?"

A small aircraft that flies autonomously with assistance from a remote source, has no pilot and no need for a cockpit or life support systems, can maneuver rapidly in response to the enemy aircraft, can make maneuvers pilots are not capable of, has no need of self-preservation and will do whatever is necessary to destroy the enemy? We already have something similar, it's called a radar-guided missile

1. G-limits dictated by airframe & payloads, not the human. Eg, F/A-18E/F & F-35C are limited to 7.5 g's; F-16 is limited to ~5-7 g's with drop tanks.
2. Life support is a small fraction of total a/c weight
3. A survivable & effective a/c (manned or no) will still cost a lot. In many ways, 5th gen a/c are already flown by [albeit narrow] AI.
4. Testing a complex, modern 5th gen a/c is time-taking. Replacing a well-tested meat brain with an e-brain will add more testing, not less.
5. NATO doctrine is domination, not attrition. Kamikaze-like is unlikely.

Also, maneuverability is both a) very expensive (eg, stronger+heavier airframe, larger wings, a second engine or more powerful engine(s), and/or thrust vectoring) and b) losing relevance in modern air to air combat, so 6th gen fighters could very well be less maneuverable than 5th gen ones.

One advantage of an autonomous UCAV over a manned fighter is that it can be made a lot smaller, and therefore less easily detected. This factor alone would probably prove decisive in some situations, particularly at low level, where in the future UCAVs may well be engaged in missions against ground targets, and where the manned fighter's radar and other sensors are least effective due to ground clutter.

We're nowhere near good enough with our AI for a computer simulant to best a human pilot in a dogfight unless the odds are further stacked against the human (computer flies a superior aircraft, computer has enhanced knowledge of "reality", computer has advantage in numbers, computer ignores physical limitations of plane or pilot without consequence). Most computer pilot AIs in combat sims are some combination of the very simplistic "locate your opponent, put your lift vector on him and pull up hard" and the more complex "human is doing this, so the best counter-move is this". There's also no small amount of "I am a game, the purpose of my existence is to be enjoyable for the human, so while I must present a challenge, I must not require my human to attend a year of combat flight school before he stands a chance".
These are the basics of ACM taught to every fighter pilot, however these strategies will get you shot down against a competent human pilot every time, for two reasons:

"Line up and pull up" tends to settle you into a horizontal "one-circle" turning fight to conserve energy. In that fight, the first pilot to realize it's happening and pull vertical can tighten the turning radius by trading speed for altitude, getting inside and cutting across his opponent's turning circle for a good if somewhat high-offset firing chance. If the opponent sticks with "line up and pull up" he will do just the opposite, trading altitude for speed, increasing his turning radius and putting his tailpipe in front of his opponent's nose.

Moves and countermoves in air combat are a fluid dance that computers are plain bad at. Computers can beat humans in chess because the number of valid moves is fairly low, so the computer can calculate the most advantageous chain of several dozen moves quickly. However, computers are relatively bad at Go, because both the total game tree complexity and the available moves on each player-turn are massive.
Air combat is similar; while there are a few basic strategies, there are infinite possibilities, and because air combat, though "turn-based", involves a different kind of "turn" from those in chess or Go, the computer doesn't get to sit there and think about its move for several seconds; it has to make the best move it can think of in a fraction of a second or else the human will get to make several "moves" before the computer reacts to the first one, and the way computers think, making it decide quickly usually boils down either to simplifying the decision-making or deciding in a random way.

Prioritization is still an area where computer AI is weak. Against one opponent, where your objective is to shoot that opponent down, a computer could do quite well. Facing the primary mission objective of completing a bombing run, with potentially hundreds of aircraft in the sky and thousands of military (and civilian) ground vehicles and people in a combat theater, making the decision of what object deserves your primary attention any given second is something even human pilots don't always do well. Most AIs in combat sims are fairly scripted; either the purpose of an enemy's existence is to shoot down the player, or it focuses on its mission until it cannot ignore the player. Real combat is somewhere in between, especially when your mission is something like CAS or BARCAP where your job isn't one fixed point on the ground or one plane in the air.

Now, computers have some advantages that are considered "cheating" in combat sims but would apply to an unmanned fighter against a manned one. First is the ability to sustain maneuvers in excess of a human's G-limit. As long as the airframe can handle it, the computer can pull 12g turns, or -12g, whatever. Second is that the weight of a human, plus the "man-machine interface" of the cockpit systems, is greater than the mass of a computer directly connected to the instrumentation. The computer is also much faster at working with the aircraft's systems than a human could ever be, so a computer pilot, within a couple seconds of seeing a "blip" on the radar, could have the target locked up, while a human, given the same blip at the same time, would still be slewing tracking gates in the B-scope.
A third big advantage is 720* visibility. Humans have about a 170* "cone" of visual response, and a fairly poor 5-10* window of actual focus and acuity. With an unmanned craft, we can install cameras covering virtually 360* around the aircraft in the horizontal and vertical, and have the computer monitor and track objects within the full field of vision, as well as in IR or other non-visible light spectrums, much more efficiently than a human could do the same with the same camera systems.
Therefore, the first fully unmanned combat aircraft is very unlikely to look or work like a manned one, because its designers will have done things that would be bad decisions in a manned craft, but will give the computer a maneuverability, speed or visibility advantage that could compensate for more simplistic decision-making of the AI.

The first advantage is numbers. Being able to put more weapon platforms in the air (and keep them almost indefinitely) is key to winning the attrition game (cue Lanchester's square law).

Excellent answer. Any comments about a remotely human controlled drone? It seems to have a hybrid of the features you discussed. i.e. A human can overcome AI limitations while still getting the advantage of high G manouveres & weight reduction. Multiple human controllers dealing with weapons / flight or different sectors might also alleviate the cone of vision restrictions. OTOH, you lose out on the fast response time of a true unmanned drone.

Ah, didn't notice that I got put on hold. Too bad. I was hoping to hear your insights about remotely manned drones.

Anyone who believes that a computer can't fly an aircraft in combat has probably never played Microsoft Combat Flight Simulator or one of the more recent air to air combat PC games. As a general principle, if a computer can manoeuver an aircraft realistically in virtual space, it can also do it in reality. In fact, computer systems should be able able to control and co-ordinate UCAVs in combat in ways that human pilots would find impossible.

@JSouthworth MFS and other flight simulators cheat because they totally control the environment. They know in absolute terms where every point of interest is. They can not only predict the wind 500 yards in front of the aircraft, the computer can ignore it if you aren't paying close attention to simulated control inputs. Similarly, planes you aren't looking at closely enough to tell they're simulated will stop pitching and banking through the virtual space and just point and move.

Saying AI can pilot drones with ease because they've been doing it in MFS for decades is like saying designing fully articulated walking robots should have been trivial because Quake was out 30 years ago. If you actually believe that, you have no clue.

KeithS, you have a point, in combat simulators the same computer controls the environment as controls the opposing aircraft, but that's a minor issue and one which you could in principle easily solve by using two independent computers, one to control the environment and one for the enemy aircraft.

Nobody would claim that Microsoft Combat Flight Simulator 98 is totally realistic, fighter aircraft in World War Two didn't have radar gunsights for one thing but the realism of the manoeuvering and tactics is good, fly the Mark 1 Spitfire against a formation of Me110s, attacking from the rear and you'll be impressed by the tactics they use to get on your tail. I wouldn't rate a manned fighter's chances against a bunch of UCAVs at low level.


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Why/when is the blunt nose better?
Most large aircraft and some fighters have blunt, rounded nose cone. OTOH many fighters (that don't use the nose for air intake) and notably the two supersonic airliners (Concorde, TU-144) have the sharp tip for a nose cone.
What is the aerodynamic justification for that? What advantages and disadvantages does the "blunt" nose cone provide - or why don't all airplanes have the sharp spike nose cone (which "feels" like the obviously optimal aerodynamic choice - obviously that "feel" is somehow flawed?)

In subsonic flow the air can react to the approaching vehicle since the pressure field around it extends forward, too. This means that a suction area on one side of the fuselage or wing will already start to pull molecules in before they reach the vehicle itself which causes this suction. A round nose allows the flow to come from a range of angles without creating too much drag. Aerodynamically speaking, the stagnation point can be moved without problems.
In supersonic flow, the air has no indication of the approaching vehicle. The first contact will cause a sudden change in direction, called a shock. For drag reduction it is important to make the shock as weak as possible, which means that the change in direction should be as small as possible. This can best be achieved by a slender, pointy tip.
Note the downward position of the intake cone of the SR-71 engine nacelle in the picture below: It is angled so that at Mach 3.2 the cone is symmetrical to the oncoming flow (which gives you a pretty good indication of the angle of attack of the whole plane).

SR-71 during take-off (picture source). Not only is the cone angled downward, but also canted in because the flow is pressed sideways by the aircraft's forebody in supersonic flight.
In hypersonic flow (Mach > 5) a blunt nose might again be preferable if the nose's materials put an upper limit on aerodynamic heating. A pointed tip will produce an attached shock which will heat the tip to something close to the stagnation temperature of the flow. A blunt nose, however, will cause a separated shock. This creates more drag and a higher amount of heat overall, but allows to spread this heat over a larger area and dump most of it into the air, producing lower peak loads. The Space Shuttle had such a blunt nose, since drag minimization is not a priority for a re-entry vehicle.

...and yet, most rockets nowadays (definitely supersonic vehicles) have blunt noses... any reason for that?

@SF: Yes, heat. The pointed tip has an attached shock with massive heat transfer into the small tip. A blunt tip will create more drag, but has a separated shock which will produce more heat overall, but lower peaks. This is only important above Mach 5, so I did not add it here since the question concerns aircraft. I answered only because I could not bear to see the rambling of aeroalias as the only answer here.

Aircraft design is full of compromises. In case of aircraft nose design, the main factor is to reduce drag. As you yourself noted, the main difference is in flow regime, i.e. subsonic and supersonic. There are different types of drag- skin (or friction) drag, form drag and wave drag (which becomes important only at supersonic speeds.
For subsonic flow, the main drag components are the first two- skin friction and form drag. Here, if we consider the fuselage to be a cylinder with the nose in front (which is a pretty good approximation), the blunt nose configuration gives a lesser drag coefficient (non-dimensional drag) compared to the conical or sharp nosed one. This means that all other things being equal, the blunt nose has lesser drag compared to sharp ones in subsonic flow. In particular, the blunt nose has lesser surface area compared to the sharp, long ones and thus lesser skin friction drag.

Image from Fluid Dynamic Drag by Hoerner
From the above figure, you can see that the blunt nose is actually better compared to a sharp nose as far as drag is concerned.

Image from Fluid Dynamic Drag by Hoerner
However, as the aircraft goes to supersonic flow, the main concern becomes wave drag. Here, the sharp nose keeps the shock wave clear of the aircraft.

Image from wotzup.com
Another thing is that in a sharp section, the cross sectional area varies gradually, which helps in prevention of local acceleration (which can result in local sonic conditions). This is the reason why you see aircraft that fly subsonic over most of their flight regime have blunt noses, while those fly supersonic over most of their flight path have sharp noses.
Of course there are other points to consider too:

The manufacturing cost of the sharp nose is usually greater than a blunt nose (has more area, for one).
A long, sharp nose will affect visibility during landings (Concorde had a droop-down nose because of this). Also, parking in airport ramps is going to be difficult.
A sharp nose will have lesser volume (for mounting radar, for example). As a result, most supersonic aircraft actually have a sightly modified nose section (elliptical or oogival, for example), especially, fighter aircraft.

Image from spaceflightsystems.grc.nasa.gov
As can be seen, an elliptical section with same base diameter and height has double the volume of a conical one. In some cases, where the nose landing gear retracts into the nose (like A350), this will be important.

On a different application, I suppose this would also explain why handgun bullets are blunt-tipped whereas rifle bullets are pointed.

@TomMcW: Look for articles on "spitzer bullets": They originated in France in the 1880s and were remarkable for their much longer range.